(A) In association with the tendency for higher degree of integration and higher performance in the field of semiconductor devices, there are demands for a manufacturing device which can satisfy the needs, there have been made intensive efforts for creating a higher degree of vacuum and cleaner atmosphere for forming a film.
In order to create an ultra-high degree of vacuum and ultra-clean atmosphere for forming a film, it is required to completely suppress out gas discharged from the manufacturing device (e.g., a process device for forming films or the like) as well as from the internal surface of a fluid supply piping system for gas or the like.
With years of research and development activities by the present inventor, now it is possible to form an oxide passivated-film on a surface of the device or the like containing therein chromium oxide as a main element which is excellent in corrosion resistance and emits only an extremely small amount of out gas therefrom. As a result, the present inventor has succeeded in creating a supply gas as well as an atmosphere for forming a film in which out gas discharged from inside of the device is suppressed to a rate so that the gas is hardly detected by any of current measuring devices. Namely, it is possible to suppress a density of impurities (moisture, hydrocarbons or the like) in the supply gas as well as in the atmosphere for forming a film to not more than the order of ppb and further to the order of ppt.
However, in accordance with the tendency that devices become increasingly larger in size and more complicated, there have been more and more intense needs for constructing a fluid piping for gas, chemicals or the like as well as a manufacturing device for a semiconductor or the like with materials to be welded each having an oxide passivated-film with chromium oxide as a main element thereof formed thereon made by cutting a long-sized member having an oxide passivated-film with chromium oxide as a main element thereof formed thereon to a specified length, and by connecting the materials to be welded to each other by welding.
It should be noted that conventionally the member is cut with a manual pipe cutter. Then, after the material is cut, the cut edge faces are further smoothed with bite by a specific edge-face processing device (produced by Tritool) to remote burrs due to the cutting, and also the roughness of the surface is made to be fine.
The cutting and the smoothing are executed while inert gas such as N.sub.2 gas or the like as purge gas is flown onto the surfaces being cut to prevent deposition of particles from outside as well as of chips generated when the material is cut onto the surfaces of the material to be welded. Especially, in a case where the material to be welded is tubular, particles from outside as well as chips generated when the material or the like is cut go into inside of the pipe and are deposited on the internal surface of the pipe, so that it is especially required that the cutting is executed while purge gas is flown inside the pipe.
(B) On the other hand, even if careful attention is paid to the matter generated when the material is cut, the oxide passivated-film is eliminated when the materials are welded, so that the surface of a welded bead section is not covered with the oxide passivated-film. For this reason, gas is easily deposited on and removed from the welded bead section, which causes the supply gas to be contaminated. Further, in not only the bead section but also in both sides of the welded bead section, chromium is volatilized, whereby chromium composition therein abruptly decreases, so that the corrosion resistance is reduced, which is the fact found by the present inventor. FIG. 1 shows the state as described above, and in the figure the state is indicated by the solid line B.
Namely, as indicated by the solid line B shown in FIG. 1, the welded bead section is set to 0, and when chrome composition is measured in both sides of the section, it can be determined that the density of chromium therein is abruptly decreased.
For this reason, when there are may joints to be welded, a quantity of out gas discharged from the joints increases to an unignorable degree, whereby the atmosphere is contaminated, and realization of a ultra-high vacuum and ultra-clean atmosphere is prevented. Also in a device and a piping system each using corrosive gas or the like, a welded section and a place adjacent to the welded section are corroded, which also causes the atmosphere to be contaminated.
For this reason, the inventor has proposed a technology different from the present invention, in which an oxide passivated-film with chromium oxide as a main element thereof is formed also on the welded section by subjecting the cut surface to chromium plating and welding, and then executing processing for formation of a passivated film while gas is flown thereonto (Japanese Patent Application No. 5438/1993).
In this technology, the plated chromium has a roll of guarding chromium from being volatilized, namely this plated chromium is oxidized by oxidizing gas due to heat generated when welding is executed, so that the chrome composition in the welded bead section as well as in a heat affected zone is prevented from decreasing, and an oxide passivated-film with chromium oxide as a main element thereof is also formed on these zones. For this reason, with this technology, it is possible to suppress the density of impurities in supply gas or an atmosphere for processing to not more than the order of ppb and further to the order of ppt even in the fluid supply piping having a welded section as well as in the manufacturing device for a semiconductor or the like.
(C) However, the present inventor has found that the problems as follows occur even in the technology described above.
(1) There is sometimes a case where an abnormally large number of particles are generated when welding is executed. Namely, as shown in FIG. 5, the problem described above has been found as a result of welding in a butt joint while back shield gas (B.S.G.) is being flown inside the tubular material to be welded (a sample) and counting generated particles with a particle counter in the downstream from the B.S.G.
The generated particles are deposited on the surface of the material to be welded, and the material is used for construction of a process device or the like as it is, then, the deposited particles on the surface is removed therefrom, for instance, when the gas is flown during formation of a film, and is brought into the atmosphere for forming the film.
(2) Also, particles go into the melting section, which causes the strength of the welded section to be reduced.
(3) It is sometimes impossible to suppress the density of impurities such as moisture or the like to the order of ppt. Namely, so far as realization of a ultra-clean atmosphere is concerned, the repeatability of this technology is not always good.
It is an object of the present invention to provide a material to be welded for butt welding which can reduce a quantity of particles going into a welded section after the welding is executed, and also to provide a method of cutting the same.
It is another object of the present invention to provide a material to be welded for butt welding which can construct a piping or a device each being capable of realizing with high-repeatability or ultra-clean atmosphere in which the density of impurities such as moisture or the like can be suppressed, and a method of cutting the same.
It is still another object of the present invention to provide a material to be welded for butt welding excellent in strength in the welded bead section and a method of cutting the same.
It is still further another object of the present invention to provide a wire used for wire cut electric discharge machining which can prevent reduction of chrome composition in a place adjacent to the welded bead section after the welding is executed.